Method and System for Multisample Antialiasing

1. A method for generating three dimensional computer graphics images using multisample antialiasing by sequentially processing a plurality of primitives, comprising: dividing at least a first pixel into a plurality of sample areas; processing a first primitive, by determining that all the sample areas of the first pixel are located within said first primitive, storing a value for the first primitive in a multisample memory for a smaller number of the sample areas of the first pixel than the total number of the sample areas of the first pixel, and storing data indicating that all the sample areas of the first pixel are located within the first primitive; subsequently processing a second primitive, by reading the stored data for the first pixel to determine that all the sample areas of the first pixel are located within the first primitive, determining that only some of the sample areas of the first pixel are located within the second primitive, determining whether the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, if it is determined that the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, storing a value for the second primitive in the multisample memory for each sample area of the first pixel which is located within the second primitive without reading from the multisample memory the value for the first primitive; and if it is determined that the value for the first primitive is not already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, reading from the multisample memory the value for the first primitive, writing to the multisample memory the value for the first primitive for each sample area of the first pixel which is not located within the second primitive for which the value for the first primitive is not already stored, and storing a value for the second primitive in the multisample memory for each sample area of the first pixel which is located within the second primitive.

2. A method according to claim 1 , wherein the smaller number of the sample areas of that pixel is one.

3. A method according to claim 1 , wherein the value for the first primitive and the value for the second primitive comprises a colour value.

4. A method according to claim 1 , wherein the data indicating that all the sample areas of the first pixel are located within the first primitive comprises a flag.

5. A method according to claim 4 , wherein the flag comprises a single bit.

6. A method according to claim 1 , comprising: determining that the first pixel is transparent for a third primitive; and storing a value in the multisample memory for each of the sample areas of the first pixel.

7. A method according to claim 1 , further comprising: updating the data indicating that all the sample areas of the first pixel are located within the first primitive to indicate that only some of the sample areas of the first pixel are located within the second primitive.

8. A method according to claim 7 , further comprising generating a final pixel value for rendering for the first pixel based on the values for the sample areas of the first pixel stored in the multisample memory and in dependence on the updated data for the first pixel.

9. An apparatus for generating images from 3-D image data using multisample antialiasing in sequential processing of a plurality of primitives from the 3-D image data, comprising: a non-transitory memory; a processor unit coupled with the non-transitory memory and configured for processing a first primitive by dividing a first pixel into a plurality of sample areas, determining that all the sample areas of the first pixel are located within said first primitive, storing a value for the first primitive for a smaller number of the sample areas of the first pixel than the total number of the sample areas of the first pixel, and storing data indicating that all the sample areas of the first pixel are located within the first primitive; said processor unit being further configured for subsequently processing a second primitive by reading the stored data for the first pixel to determine that all the sample areas of the first pixel are located within the first primitive, determining that only some of the sample areas of the first pixel are located within the second primitive, determining whether the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive; in response to determining that the value for the first primitive is already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, storing a value for the second primitive for each sample area of the first pixel which is located within the second primitive without reading the value for the first primitive from the multisample memory; and in response to determining that the value for the first primitive is not already stored in the multisample memory for each sample area of the first pixel which is not located within the second primitive, reading the value for the first primitive from the multisample memory, writing the value for the first primitive to the multisample memory for each sample area of the first pixel not located within the second primitive for which the value for the first primitive is not already stored and storing a value for the second primitive for each sample area of the first pixel which is located within the second primitive.

10. The apparatus according to claim 9 , wherein the processor unit comprises one or more programmable processors.

11. The apparatus according to claim 9 , wherein the processor unit comprises an input processor, an output processor and a multisample processor.

12. The apparatus according to claim 9 , wherein the smaller number of the sample areas of the first pixel is one.

13. The apparatus according to claim 9 , wherein the value for the first primitive and the value for the second primitive comprises a colour value.

14. The apparatus according to claim 9 , wherein the data indicating that all the sample areas of the first pixel are located within the first primitive comprises a flag.

15. The apparatus according to claim 14 , wherein the flag comprises a single bit.

16. The apparatus according to claim 9 , wherein the processor unit is further configured for determining that the first pixel is transparent for a third primitive; and for storing a value in the multisample memory for each of the sample areas of the first pixel.

17. The apparatus according to claim 9 , wherein the processor unit is further configured for updating the data indicating that all the sample areas of the first pixel are located within the first primitive to indicate that only some of the sample areas of the first pixel are located within the second primitive.

18. The apparatus according to claim 17 , wherein the processor unit is further configured for generating a final pixel value for rendering for the first pixel based on the values for the sample areas of the first pixel stored in the multisample memory and in dependence on the updated data for the first pixel.